Etching of metals, and particularly of copper, is carried out in a large number of industrial processes, both for the cleaning of copper surfaces, and in order to provide a desired pattern on the copper surface. An example of the application of the later technique is in the production of "printed circuits" in which a layer of copper on an insulated substrate is etched away in predetermined areas to provide a desired pattern of conducting copper on the surface of the insulating substrate.
Copper which is used in printed wiring board (PWB) or printed circuit board (PCB) fabrication often is etched prior to processes such as the application of resists or the application of bonding agents such as oxides, immersion tin, or coupling agents such as silane. The etching results in a physical roughening of the copper surface which provides increased surface areas for bonding.
A variety of etching compositions have been suggested in the prior art for the production of printed circuit boards, and these etching compositions include ferric chloride, cupric chloride, various ammoniacal etchants, etc. More recently, etching compositions which comprise mixtures of an acid such as sulfuric acid and oxidizing agents such as hydrogen peroxide have been developed and utilized. The advantages of the peroxide sulfuric acid system include competitively low cost and in situ recovery of copper from the used etching composition in the form of copper sulfate or copper metal. The composition from which the copper has been recovered can be regenerated by replenishment of the hydrogen peroxide. Such etching compositions provide for the recovery of valuable copper and minimize the environmental burden otherwise arising from the disposition of used etching compositions. Various sulfuric acid/hydrogen peroxide etching compositions are described in, for example, U.S. Pat. Nos. 3,801,512, 4,130,454, 3,668,131 and 3,463,733.
It is an ongoing problem to bond organic materials to metal surfaces such as copper. When the bond between the metal surface and an organic material is exposed to heat, delamination may occur. Multilayer printed circuit boards (PCBs) are typically constructed by interleaving imaged conductive layers, such as one containing copper with non-conductive layers such as a partially cured B-stage resin (i.e., a prepreg) into a multilayer sandwich which is then bonded together by applying heat and pressure. The conductive layer, i.e., the copper circuitry, does not bond well to the non-conducted B-stage resin prepreg. Often, intermediate layers are used to bond the B-stage prepreg to the copper circuitry.